Piano apparently sketched his idea on a restaurant napkin while meeting property developer Irvine Sellar in March 2000. According to Piano's architectural firm, RPBW, Sellar keeps the famous napkin in his offices. "He saw the beauty of the river and the railways and the way their energy blended and began to sketch in green felt pen on a napkin what he saw as a giant sail or an iceberg," Sellar recalled in a recent interview.
— guardian.co.uk